1. Field of the Invention
This invention relates generally to a grinding machine, and more particularly to a grinding machine with a truing device for truning a grinding wheel made of hard abrasive grain such as, for example, cubic boron nitride (CBN), diamond or the like.
2. Description of the Prior Art
In a known grinding machine incorporating a digital feed controller, there are provided digital switches for setting control data such as, for example, feed amount, feed rate, dwell time and the like, and the feed movement of a wheel carrier is controlled by a stepping motor in accordance with the control data. The wheel carrier is moved between a transient original position and an advanced position in a grinding operation, and the transient original position is compensated for a reduction in radius of a grinding wheel each time the same is trued. The memory of the transient original position is lost at the occurrence of an interruption of electric supply or an emergency stop. In order to return the wheel carrier to the transient original position, an absolute original position is provided, and when a re-starting is made after the interruption of electric supply or the emergency stop, the wheel carrier is once retracted to the absolute original position and then, is again returned to the transient original position by being advanced by a distance between the absolute and transient original positions which distance is memorized in a fixed memory device such as, for example, a core memory unit or a latch relay circuit.
CBN grinding wheels are being increasingly applied to grinding machines of the above-noted type wherein an importance is placed not only upon machining efficiency but also upon machining accuracy, though for many past applications of the CBN grinding wheels emphasis has been placed only upon machining efficiency, as in cutting operation. In an application of the CBN grinding wheel to such a digital control grinding machine, however, it is desirable to arrange a truing device for the CBN grinding wheel upon the work table or the machine bed since the CBN grinding wheels have a long tool life and do not require truing operations as frequently as do other less durable grinding wheels. Furthermore, in truing the CBN wheel, it is important to precisely infeed the CBN grinding wheel since CBN grinding wheels are quite expensive.